Reciprocating vacuum pump



Oct 7,1969] was 3,471,079

nmciraocmme VACUUM PUMP Filed Sept. 21; 1967 I -7 Shets-Sheet 1 INVENTQR.

51mm MYERS Arra /vim Oct; 7, 1969 v E. B. MYERS 3 7 v RECIPROCATING vacuum PUMP I v Filed Sepi. 21, 1967 Y 7 Sheets-Sheet 2 INVENTOR.

' flrrok/veys Euva/v' a. MYERS Oct. 7, 1969 E, a. Y S V 3,471,079

RECIPROOATING VACUUM PUMP Filed Sept. 21, 1967 v Sheets-Sheet i v x n NI 54/10 5. NYE/F5 tum Oct. 7, 1969 a. s. MYERS REOIPROCATING VACUUM PUMP 7 Sh eetsSheet 4 Filed Sept. 21. 196? Oct. 7, 1969 E. a. MYERS I 3,471,079

I REOIPROCATING VACUUM PUMP Filed Sept. 21, 19s? 7 Sheets-Sheet 8 3- 6W Wm j AVE I N VEN TOR. um/v a. MYERS QWQ WK Oct; 7, 1959 Filed Sept. 21. 1967 v E. B. MYERS nscxraocume mm rum &

I 7 sheets -spei '7 NVENTOR.

5. NYE/95 United States Patent 3,471,079 RECIPROCATING VACUUM PUMP Elman B. Myers, Wayne, NJ. (Box 1216, Preakness, NJ. 07470) Filed Sept. 21, 1967, Ser. No. 669,552 Int. Cl. F04b 35/00, 27/02 US. Cl. 230-53 34 Claims ABSTRACT OF THE DISCLOSURE A vacuum pump having a cylinder with a free and a driven piston with the driven piston being connected to a reciprocating drive and one end of the cylinder being provided with means, such as a bounce chamber, for urging the free piston toward the driven piston. Inlet and exhaust ports are provided in the wall of the cylinder.

FIELD OF THE INVENTION This invention relates to a novel reciprocating vacuum pump. More specifically, it relates to a novel reciprocating vacuum pump having a free piston and a driven piston.

DESCRIPTION OF THE PRIOR ART The need for an improved and contaminate free mechanical vacuum pump has existed to the present and especially in connection with the need for improved fore pumps for use with current high vacuum devices such as titanium sublimation vacuum pumps.

Some presently available vacuum pumps require an undesirably long time to achieve a high vacuum. Others employ liquid lubricants, sealants or other operating fluids which may contaminate the gas being pumped by backstreams into the high vacuum region. Many vacuum pumps can only pump a portion of the gas within the pump during one cycle of operation. Consequently such pump must be subjected to a great number of cycles of operation to fully expel gas within the pump at any given time. Other pumps employ complicated valving means to control the intake and exhaust of the gas being pumped. Still other pumps provide continual rather than intermittent suction and may not be conveniently used for applications in which an intermittent suction is desirable.

SUMMARY OF THE INVENTION It is one object of this invention to provide a vacuum pump which expells all of the gas within the pump cylinder by a single stroke of the pump piston.

It is another object of this invention to provide a vacuum pump which may operate without liquid lubricants, liquid sealants or other operating fluids.

It is still another object of this invention to provide a vacuum pump for pumping a gas, such as noble gases, without contaminating the same.

It is an additional object of this invention to provide a vacuum pump suitable for use with pulsating loads.

It is a further object of this invention to provide a vacuum pump in which a driven piston mates with a free piston, thereby voiding a gas chamber formed therebetween.

It is a further object of this invention to provide a vacuum pump in which the piston can be selectively controlled with respect to its radial clearance with the cylinder.

It is a further object of this invention to provide a vacuum pump which may be operated individually; or which may be coupled to a second similar pump such that the two pumps function in parallel as a single pumping means with double displacement ability; or which may be coupled to a second similar pump such that the two "ice pumps function in series to provide a synchronous twocycle pumping operation.

-It is a further object of this invention to provide a vacuum pump which may be coupled to operate with a second similar pump such that the second pump automatically seals off the gas in the first pump.

It is also an object of this invention to provide a vacuum pump characterized by a high through-put and by simplicity and efiiciency of operation.

Speaking generally, the invention comprises a pump having a cylinder with a free and a driven piston, the driven piston being connected to a reciprocating drive, and one end of the cylinder being provided with a bounce chamber. Upon movement of the driven piston toward the free piston, the free piston moves toward the bounce chamber and compresses the gas in the bounce chamber. =Upon movement of the driven piston away from the free piston, the gas compressed in the bounce chamber expands and moves the free piston in the same direction as the driven piston. A stop connected to a control rod for the free piston limits the extent to which the expanding gas may move the free piston. When the stop arrests the free piston and the reciprocating drive withdraws the face of the driven piston from the face of the free piston, a void is formed between the two pistons. When the driven piston uncovers an inlet port in the side of the cylinder and permits gas to enter the chamber formed between the confronting faces of the two pistons, the reciprocating drive then reverses the direction of the driven piston thereby closing the inlet port and compressing the gas in the chamber. As a result of the compression, force transmitted to the free piston causes it to retract and eventually uncover the exhaust port. The gas in the chamber between the faces of the two pistons then exhausts through this port until the face of the driven piston abuts with the face of the free piston. The cycle is then repeated, the driven piston and free piston maintaining interfacial contact until the exhaust port is closed by the free piston and another voiding operation begins.

The invention also comprises coupling a plurality of pumps of the type described to operate in cooperation with one another. Thus, in one such embodiment, the driven pistons of two horizontally-opposed pumps are connected to a scotch yoke which provides synchronous rectilinear reciprocation of the pumps driven pistons.

In another embodiment, the driven pistons of two horizontally-opposed pumps are actuated by a common, double-acting reciprocating cylinder which is controlled by pressure switches at the pumps bounce chambers. A pump of the type described may be coupled with a second similar pump to function in unison as a single pulsingtype pumping means with twice the displacement of a singlepump, or to function alternately as a two-cycle pumping means.

In still another embodiment the pistons are internally pressured to expand the pistons and select their radial fit with the Cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of this invention will become apparent from the following detailed description of the invention taken in conjunction with accompanying claims and drawings, in which:

FIG. 1 is a plan view of an embodiment of the invention having two horizontally-opposed pumping assemblies driven by a common driving means;

FIG. 2 is a fragmentary horizontal section view of the pump of FIG. 1 showing the two horizontally-opposed gumping assemblies connected to a common scotch yoke rive;

FIG. 3 is a fragmentary horizontal section view of the right-hand pumping assembly of FIG. 2 prior to the discharge through exhaust ports of gas between the two pistons of the pumping means;

FIG. 4 illustrates the apparatus of FIG. 3 immediately subsequent to the discharge of gas through the exhaust ports;

FIG. 5 illustrates the apparatus of FIG. 3 during the first part of the return stroke of the pistons;

FIG. 6 illustrates the apparatus of FIG. 3 during the portion of its cycle of operation when gas may enter the chamber between the pistons through an inlet port;

FIG. 7 is a fragmentary perspective view, in crosssection, of an end of a driving piston of the embodiment of FIG. 2, showing a dry lubricant bonded to the outer surface of the piston;

FIG. 8 is a fragmentary vertical section view of an embodiment of the invention shown in FIG. 1 and having two horizontally-opposed pumping assemblies driven by a common driving means which includes an electric motor and a scotch yoke.

FIG. 9 is a fragmentary vertical section view of an embodiment of the invention in which two horizontallyopposed pumping assemblies are driven by a doubleacting reciprocating drive piston;

FIG. 10 is a fragmentary vertical section showing the double-acting drive piston of FIG. 10;

FIG. 11 is a schematic representation of the control system for the drive piston of FIG. 10;

FIG. 12 is a fragmentary elevational view of the embodiment of the invention shown in FIG. 9 which illustrates various hydraulic components for driving the vacup p;

FIG. 13 is a hydraulic schematic of hydraulic corn- 7 ponents of the embodiment of FIG. 9;

FIG. 14 is a vertical section view showing a piston arrangement for the free or driven piston of the pum of the invention;

FIG. 15 shows the piston arrangement of FIG. 14 in an internally pressured condition;

FIG. 16 is a vertical section view showing a piston arrangement adapted for use in internal combustion engines or compressors, and

FIG. 17 is a vertical section view showing the piston arrangement of FIG. 16 in an internally pressured condition.

FIG. 18 is an enlarged fragmentary vertical section view showing a hard coating applied to the piston.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figures, FIG. 1 is a plan view and FIG. 2 a fragmentary horizontal section view of an embodiment of the invention having two horizontallyopposed pumping assemblies 20, 2-0 driven by a common scotch yoke 22 within a drive housing 24. The drive shaft 26 of a gear reducer 28 whish is coupled to the output shaft of a variable-speed electric motor 30 (Confer FIG. 8) drives the scotch yoke 22. Shaft 26 is secured to a bushing 32 at the center of an annular flywheel 34 by means of a set screw 36 and a key 38. Pivotally mounted on flywheel 34 is a roller 40. Roller 40 is disposed between two spaced-apart ways 42, 42' of a crosshead member 44 which also has two bifurcated end portions 46. These end portions of crosshead member 44 are slidably mounted to a pair of spaced-apart parallel shafts 48 by means of ball bushings 50 which permit movement of each end portion 46 along its respective shaft 48. Shafts 48 are mounted to housing 24 within bosses 54 in the wall of the housing. The central portion of each of the spaced-apart ways 42, 42' of the crosshead member is connected to the ends of the drive rods 56, 56' of the horizontally-opposed pumping assemblies 20, 20.

In this embodiment of the invention, shafts 48 are disposed parallel to drive rods 56, 56', and ways 42, 42 of the crosshead member are disposed perpendicular .4 thereto. Further, the axis of rotation of flywheel 34 is the point on the line of the coincident longitudinal axes of drive rods 56 and 56 which is equidistant from their facing ends.

Upon a rotation of drive shaft 26, which for purposes of illustration may be assumed to be in a clockwise direction viewed in FIG. 2, flywheel 34 and roller 40 also rotate in a clockwise direction. Roller 40 is, however, constrained between the spaced-apart ways 42, 42' of the crosshead member, and it therefore pulls the crosshead member first to the right, then to the left and then repeats the cycle as the flywheel rotates. This imparts a rectilinear reciprocating motion to the drive rod 56, 56' connected to the midpoint of the crosshead member. If the flywheel rotates uniformly with a constant angular velocity, the drive rods will move in a simple harmonic motion along their longitudinal axes.

Considering the right-hand pumping assembly 20 in FIG. 2, as mentioned, one end of drive rod 56 is connected to the midpoint of crosshead member 44. Its other end is connected to the center of a coaxial, driven piston 58 slidably contained within a pump cylinder 60. Also contained within the pump cylinder is a free piston 62 having a free piston control rod 64. Free piston 62 is both slidable and rotatable with respect to the inner Wall of its cylinder, and has a close fit therewith. An end member 66 is bolted to the pump cylinder to provide a transverse end wall 68 for the cylinder as well as a bounce chamber 70. Member 66 is attached to a flange on the end of pump cylinder 60 by means of bolts 72 and a sealing ring 74 which provides an airtight connection. Piston rod 64 is slidably and rotatably mounted to the wall portion 68 of member 66, and a lock nut 76 is threadedly attached to the end of the piston rod Within the bounce chamber to act as a stop member to control the axial movement of the free piston control rod. The will portion of member 66 has a plurality of openings 78 therethrough.

Cylinder 60 is secured to housing 24 by means of bolts 80 and sealing rings 82. The cylinder has an inlet port 84 and a plurality of exhaust ports 86 in its longitudinal wall. A supply tube 88 is connected to the cylinders inlet port by means of bolts 90 passing through a flange on the end of tube 88. A sealing ring 92 is also provided to provide an air-tight connection. The other end of supply tube 88 is connected to one end of a header or cross-connect tube 94, another end of which is connected to the supply tube 88 for the horizontally-opposed pumping assembly 20'. An intermediate point of the cross-connect tube is connected to a common gaseous supply (not shown), i.e., the container or vessel from which gas is to be evacuated.

Considering now a typical sequence of operation of pumping assembly 20, FIG. 3 illustrates pumping assembly 20 of FIG. 2. prior to a discharge through exhaust ports 86 of gas between the face of driven piston 58 and the confronting face of free piston 62. In FIG. 3, driven piston 58 is being moved toward the right by scotch yoke 22 and drive rod 56, compressing the gas in the chamber 96 defined by the faces of the pistons as well as forcing free piston 62 to also move to the right, thereby forcing the gas 'behind free piston 62 and in bounce chamber 70 to be compressed. The gas behind free piston 62 communicates with that in the bounce chamber through openings 78 to maintain a balance of pressure. When exhaust port 86 is uncovered by free piston 62 and chamber 96 is brought into communication with port 86, the gas in chamber 96 exhausts through the port and the confronting faces of pistons 58 and 62 snap together as shown in FIG. 4. Since the faces are controlled to be perfectly square to the cylinder axis and have smooth surfaces, the faces uniformly mate with one another and no gas remains between them.

As the flywheel 34 of the scotch yoke continues to rotate, drive rod 56 pulls the driven piston to the left,

as shown in FIG. 5. The compressed air in the bounce chamber and behind the free piston then also expands and moves the free piston to the left in contact with the driven piston and past the exhaust ports 86, carrying piston rod 64 with it. The free and driven pistons maintain a common interface until the exhaust port is valvedoff by the free piston. Free piston 62 may continue to move to the left until the stop 76 on the free piston control rod contacts the wall portion 68 of member 66, at which time it stops. Since the driven piston continues to move, a void is created between the pistons. As shown in FIG. 6, the driven piston continues to be pulled to the left by drive rod 56 and uncovers inlet port 84, al lowing gas to enter the chamber 96 between the faces of the two pistons. As the flywheel 34 of the scotch yoke continues to rotate, drive rod 56 then drives piston 58 to the right, as shown in FIG. 3, and the cycle is repeated.

As is illustrated in FIGS. 3-6, the gas received from inlet port '84 by the chamber formed by the confronting faces of the pistons undergoes transit compression as the chamber is moved into communication with exhaust ports 86. When the exhaust ports are valved-open by the free piston and the gas in chamber 96 is discharged through the ports, pistons 58 and 62 meet to form a common interface, voiding chamber 96 and expelling the gas which had been trapped in this chamber with a single stroke of the driven piston. The confronting faces of pistons 58 and 62 are flat and have a high degree of surface finish, so that when they come into interfacial contact no gas remains between them.

When driven piston 58 reverses in direction, as shown in FIG. 5, free piston 62 is pressed against the driven piston and advanced sufficiently to close off exhaust ports 86 by the resilient loading of the compressed gas in the reaction or bounce chamber 70. Further, since the gas formerly in chamber 96 has been expelled, the free piston will also tend to follow the driven piston due to the force of atmospheric pressure urging the two pistons together in opposition to any tendency of the faces to separate.

As the driven piston continues to retract after the free piston has closed off the exhaust ports, the free piston is arrested in its travel by the snubbing action of stop 76, and a chamber 96 is once again formed between the faces of the pistons. As all of tthe gas formerly between these pistons 58, 62 has been expelled, gas from header 94 enters voided chamber 96 very rapidly when the inlet port 84 is valved open by the driven piston. In this way the pressures between header 94 and the chamber equalizes and achieves a static balance. The higher the pressure of the gas in the header, the more rapid will be the entry of gas into chamber 96.

As mentioned above, chamber 96 and the gas contained in the chamber is compressed in transit before it is discharged through ports 86. (See FIG. 3.) This being so, a greater pressure differential is also caused to exist between that of the gas in the chamber and that in the exhaust line, and a more rapid expulsion of the gas is effected than would otherwise be the case.

If desired, a rubber tube, a coil spring or an equivalent resilient member may be used to augment or to substitute for the resilience of the compressed gas in the bounce chamber for regulating the stroke of the free piston and the free piston control rod. Thus, a spring or other resilient member may be mounted to the free piston control rod between the stop member and its coacting stopping surface. The resilient member would be preloaded to hold the stop member against the coacting stopping surface until the free piston control rod is displaced by movement of the driven piston toward the face of the free piston, and to return the stop member when the driven piston changes its direction of movement and moves away from the free piston. If an automatic control in the nature of that described below with reference to FIGS. 9-12. is desired, the bounce chamber may be retained and the pressure of the gas therein monitored by pressure sensitive switches as in the embodiment referred to. If an automatic control is not desired, for example in an application where a single pumping assembly rather than cooperating pumping assemblies is used, then the bounce chamber may be relied upon to supply the required movement of the free piston.

An advantage of the use of the bounce chambers to bias the free pistons toward the driven pistons is that bounce chambers containing gas readily provide the proper elastic properties while not being subjected to the weakness of mechanical springs or members of resilient material such as rubber. Mechanical springs can become resonant at certain operating conditions and this is an undesirable condition since it affects the degree of restraint applied to the free pistons by the mechanical springs. Bulfers of resilient material such as rubber can encounter progressive deterioration during operation in response to the repeated deformation of the buffer to a relatively great extent.

The bounce chambers eliminate the problems related to other elastic restraints since the bounce chambers are sealed gas chambers formed by the pump cylinder and containing pressurized inert gas. In effect, the bounce chambers are gas springs which operate at a natural frequency established by the reciprocal movement of the driven pistons. The gas spring can be pressurized to a level which is sufficient to overcome the loads resulting from the mass inertia of the free piston and the frictional restriction of movement generated by the cylinder wall contact with the piston. As a result the bounce chambers can provide a movement to the free pistons which is in synchronism with the driven piston. This periodic forming of mechanical synchronism enables the free piston arrangement to operate successfully as a pump device.

As shown in FIG. 9, cross-connection 70a can be connected to bounce chambers 70. The cross-connection feeds back pressure charges of one bounce chamber to the other and therefore can assist in maintaining synchronism between the driven and free pistons. The low inertia of the gas flow being transmitted by the cross-connection can serve the enhance any resonance occurring in the mechanical system.

Turning to FIG. 7, it is one feature of the invention that no liquid lubricants, sealants or other operating fluids are required for satisfactory operation. In an application where an extremely close fit is desired between the contacting surfaces of the pistons 58, 62 and the cylinder 60, or where for some other reason it is desirable to reduce the coefiicient of operating friction between these surfaces, a dry lubricant which may be multi-layer, may be bonded to said contacting surfaces. FIG. 7 is a fragmentary view of the face end of driving piston 58, showing a dry lubricant 98 bonded to its longitudinal wall. In applications where it is desirable to avoid contamination of the gas being pumped, if a dry lubricant is used, it is desirable that it be chosen so as to mitigate the danger of contamination.

Any suitable material may be used for the various parts of the pump of the invention. Where steel is used, as for housing 29, cylinder 60, rods 56 and 64, or pistons 58 and 62, it is preferably vacuum-melted, high-density steel to avoid contamination of the gas in the pump by gases entrained in the pump parts. By way of example, the pistons and cylinders can be formed of AMS 52100 steel or a graphitic steel such as Graph-Mo steel produced by the Tinker Bearing Company. AMS 52100 steel is doublevacuum melted, forged, and outgassed. For the piston, alumina material can be used in place of metal to give great dimensional accuracy and substantially no wear. In addition the piston can include a core of vacuum melted steel, coated with alumina.

Turning now to FIG. 8, this figure illustrates another embodiment of the invention which is similar in may respects to the embodiment described with reference to FIGS. 1-6. Corresponding reference numerals are therefore used where appropriate.

In the embodiment of FIGS. 1-6 the inlet ports 84 of two horizontally-opposed pumping assemblies 20, 20 were supplied with gas from a common header 94 connected to the gas volume being evacuated, and the gas was then exhausted into the atmosphere through a plurality of exhaust ports 86 in each of the pumping assemblies. In the embodiment of FIG. 8, however, a single exhaust port 86 is provided for each of two horizontally-opposed pumping assemblies 20, 20, and the exhaust port of one pump ing assembly 20 is connected to the inlet port of the other pumping assembly 20' by a cross-connected manifold (not shown) between the latter two ports. The inlet port 84 of pumping assembly 20 is connected to the gas supply (not shown). Thus, instead of the two pumping assemblies providing alternating pumping of gas from a common supply, as was the case in the embodiment of FIGS. l-6, the pumping assemblies 20, 20 of the embodiment of FIG. 8 are adapted to be coupled to provide twostage pumping, one pumping assembly 20' sealing the other pumping assembly 20 011 from the atmosphere when the former is pumping, and the other pumping assembly 20 sealing the first pumping assembly 20 off from the supply when the latter is pumping. In this way, only pumping assembly 20' is opposing the pressure of the atmosphere, approximately 14.7 pounds per square inch at sea level and Centigrade, while pumping assembly 20 is opposing the reduced pressure of the volume in which it is generating a vacuum. When the terminal point is reached in the vacuum pumping ability of pumping assembly 20, this vacuum is automatically sealed otf by pumping assembly 20' and maintained by the cooperation of the two pumping assemblies.

Considering the structure of the embodiment of FIG. 8 now in further detail, as in the embodiment of FIGS. 1 and 2, two horizontally-opposed pumping assemblies 20, 20 are driven by a scotch yoke 22 coupled to a gear reducer 2'8 and a variable-speed electric motor 30. The drive shaft 26 of the gear reducer is secured to a bushing 32 at the center of an annular flywheel 34. A key 38 is provided for the drive shaft, and a counterweight 35, which may be of lead, is secured to the flywheel by means of a socket-head set screw 37 to offset the unequal weights of the moving parts of the assembly. Bushing 32 is secured to the flywheel by welds 39, and a driver wheel 41 is aflixed to the flywheel by a set screw 43. The other end of the driver Wheel is affixed to a roller 40 which is slidably mounted between two-spaced-apart ways 42', 42 of a crosshead member to provide a scotch yoke drive similar to that illustrated in FIG. 2.

The drive rods 56, 56 of pumping assemblies 20, 20 are threadedly secured to the midpoints of the Ways 42, 42'. The scotch yoke of the embodiment of FIG. 8 provides an alternating rectilinear reciprocation of drive rods 56, 56' in a manner similar to that described above with reference to FIGS. 1 and 2. The scotch yoke is contained within a housing 24 having a base cover 25 secured to it by bolts 27. Housing 24 is secured to the cylinders 60, 60' of pumping assemblies 20, 20' by means of bolts 80 passing through flange portions on the cylinders.

In each of the pumping assemblies of the embodiment of FIG. 8, the drive rod 56, 56' are threadedly secured to the center of an associated driven piston 58 slidably contained within a piston cylinder 60, 60. A single inlet port 84 and a single exhaust port 86 are provided in boss portions on the longitudinal walls of each of the cylinders 60, 60'. These ports 84, 86 have a rectangular transverse cross-section in order to allow for communication therethrough over a greater distance of travel of their associated valving piston than would be the case with a port of circular cross-section. inlet port 84 is valved by a driven piston 58 and outlet port 86 is valved by a free piston 62, in a manner as described with reference to FIGS. l-6.

The end portion of each cylinder 60, 60 is closed by an annular coupling disc 71 and a cap member 73 fastened to a flanged portion of the cylinder by bolts 75. Quad ring seals 77 are provided to make the connection airtight. A free piston control rod 64 is threadedly attached to each of the free pistons 62 and slidably and rotatably mounted in coupling disc 71. One end of piston rod 64 extends within a bounce or reaction chamber defined by cap member 73 and coupling disc 71, and this end of rod 64 has a lock nut 76 threaded thoreon to act as a stop to limit the stroke of the piston rod. Disc 71 has a plurality of openings 78 to provide communication be tween the bounce chamber and the portion of the cylinder bore behind the free piston. Further, a rubber washer 79 is mounted to disc 71 about the free piston control rod 76 to absorb shock loading and dampen noise when the movement of lock nut 76 is snubbed by disc 71. Each bounce chamber 70 is provided with a gas inlet fitting 81 for supplying a gas, such as argon, nitrogen or air to the chamber, as well as a pressure gauge 83 for indicating the pressure of the gas within the chamber.

FIGS. 9-12 illustrate a further embodiment of the invention. In this embodiment, a hydraulic drive instead of a mechanical drive is used to actuate two vertically-opposed pumping assemblies 120, Each pumping assembly 120, 120' has a drive rod 156 threadedly connected to the center of a coaxial, driven piston 158 slidably contained within a pump cylinder 160. Also contained within each pump cylinder is a free piston 162 having a free piston control rod 164 threadedly secured to it. Free piston 162 is both slidable and rotatable with respect to the inner wall of its cylinder and has a close fit therewith. Free piston control rod 164 is slidably and rotatably mounted within a coupling disc 171 which is fastened to the outer portion of the cylinder by means of bolt (not shown). Also fastened to the foot of the cylinder by the said bolts is a cap member 173 which, in cooperation with disc 171, defines a bounce chamber 170. One end of the free piston control rod extends within this bounce chamber and has a stop nut 176 threadedly secured thereon. Quad ring seals 177 are provided to make the connection between the cylinder, the disc and the cap member air-tight, and a rubber washer 179 is secured to disc 171 to absorb shock-loading and reduce noise.

The vertical arrangement of pumping assemblies 120 and 120 results in a vertical path of travel of each of driven pistons 158 and free pistons 162. As a result the side loading of the pistons with respect to the inner surface of cylinders 160 is reduced to a negligible value and therefore the wear of the cylinders and pistons can be minimized even though they are fitted with respect to one another with extremely close tolerancs.

The longitudinal walls of the driven and free pistons 158 and 162, respectively, have spaced V-shaped circumferential grooves 159, which by way of example are in the order of inch wide and inch deep. These grooves serve to relieve the outer tension or skin pull of the pistons relative to the inner surface of the cylinder and, by dividing the pistons into shorter effective lengths, to eliminate the effect of any rainbowing or other longitudinally extending imperfections in the walls of the pis tons.

As is shown in FIGS. 9-10, each drive rod 156 is secured to a cylinder rod 141 of a double-acting vertically reciprocating hydraulic cylinder assembly 143 having a piston secured to the facing end portions of the cylinder rods 141. In lieu of two separate cylinder rods 141, a single cylinder rod having a piston 145 about its midportion may also be used.

Piston 145 is slidably contained within a hydraulic cylinder 147 having stop portions 149 toward each end to coact with piston 145. Cylinder rods 141 are slidably mounted within the end portions of cylinder 147, which is in turn mounted within the cylinders of the horizontally-opposed pumping assemblies 120, 120. Quad ring seals 151, 153 are provided between the cylinder rods 141 and cylinder 147, and between cylinder 147 and cylinders 160. Each of the cylinders 160 of the opposed pumping assemblies is provided with a cross-connect port 155 between which a cross-connect, balance manifold 157 is connected. The balance manifold may be formed of flexible metallic hose.

The intake port 184 of pumping assembly 120' is connected to vessel 185, shown schematically in FIG. 9, which is to be evacuated. The exhaust port 186 of this pumping assembly is connected by a cross-connect manitold (not shown) to the intake port 184 of pumping assembly 120'. The final exhaust of the gas being pumped out through the exhaust port 186 of pumping assembly 120'. Pumping assemblies 120 and 120 are thus coupled to operate in a manner similar to the manner of operation of the embodiment of FIG. 8.

A pressure sensitive switch 187 is mounted upon each of two pumping assemblies by means of mounting brackets 189, and is in communication with the pressure within its respective bounce chamber 170 by means of piping 190 and a port 191 in the wall of the bounce chamber. Pumping assemblies 120, 120 are secured to a support bracket 192 by means of bolts 193 (FIG. 10).

Although a hydraulic means has been employed in the embodiment of FIGS. 9-12, a pneumatic, double-acting drive may also be used. It might also be noted that, although the term gas has been used in this specification to describe the medium being pumped, this term is intended to include air as well.

As shown in FIG. 9, a cross-connected equalizing line such as line 247 can be connected between the two bounce chambers 170. In this way the equalizing line can assist in the synchronizing of the movement of the free pistons. The low inertia of the gas in the bounce chambers and the equalizing line can enhance the resonance of the mechanical system and thereby improve the operation of the pump of the invention.

It is seen that, by practicing this invention in the manners described, it is possible to achieve the various objects of the invention recited herein, including the provision of a vacuum pump which expels all of the gas received by it in a single stroke of a piston and which may be readily coupled to operate either in series or in parallel with other similar pumps. It is also seen that it is possible to provide a vacuum pump which does not have liquid lubricants, sealants or other operating fluids which may contaminate the gas being pumped.

In high vacuum applications the pump of the invention requires that the piston have an extremely close fit to the cylinder. By way of an example, the total diametral clearance between the piston and the cylinder can be in the order of several millionths of an inch. To prevent leakage and to prevent the possibility of binding between the piston and the cylinder it is necessary that the close diametral clearance be maintained over a major portion of the length of the piston. In the case where the piston is formed of metal or where the piston comprises a body having a metal coating, it is possible to fit the piston to the cylinder with the very close clearances referred to above by a series of lapping operations.

Wear of the cylinder, once the piston is accurately fitted, can be minimized by applying a hard coating to the otherwise hard material from which the cylinder is formed such as, for example, AMS 52100 steel which typically has a hardness in the range of Rockwell C60. The cylinder can be provided with a hard coating such as that resulting from flame coating the cylinder with tungsten carbide, tantalum carbide or boron carbide.

FIGS. 14 and 15 show a piston arrangement which insures an extremely close fit between a free and driven piston and the internal diameter of the cylinder. Piston 230 which can be used either as the driven piston or the tree piston is in the form of a hollow cylinder having end walls 231 and 232. As shown in the drawings the cylindrical side wall portion 233 of the piston has a relatively thin wall section. As a result the application of internal pressure to the piston enables the side wall 233 to be displaced outwardly, that is it enables the piston to be inflated. As a result, where the piston is closely fitted to the cylinder, a final adjustment in the clearance between the piston and cylinder can readily be made by applying internal pressure to the piston. By way of example, the initial radial clearance of the uninflated piston can be in the order of three millionths of an inch. Upon applying internal pressure to the clearance, the radial clearance can be reduced substantially to zero so that the piston exactly fits the inside diameter of the cylinder.

As shown in the drawings, end walls 231 and 232 are provided with substantially heavy wall sections so that they are not deflected to any measurable extent when the internal pressure is applied to the piston. In this way end wall 231 can be maintained in a precise flat condition and square to the axis of the cylinder so that when end walls 231 of the free piston and the driven piston contact one another, no gas can remain between them.

End wall 232 of the piston is adapted to be connected to rod 234 which is either the driving rod of a driven piston or the rod attached to the snubber of a free piston. The fluid for pressurizing the piston is passed through port 235, check valve 236 and passage 237 which leads to the interior of the piston. Spring 238 biases check valve 236 into its normally closed position. By way of example, the inflating of the piston can be accomplished by subjecting its interior to hydraulic pressure in response to the introduction of a hydraulic fluid through check valve 236. The fluid can be selected to have thermal properties which are compatible to the operating condition of the piston. The level of hydraulic pressure that is applied to the piston is limited by the pressure which is required to close the radial clearance between the piston and the cylinder. Thus a mating fit is established without introducing an interference fit condition.

When the cylinder is formed from AMS 52100 vacuum melted steel such as that made available by the Timken Roller Bearing Company, the piston can be provided with a coating 247 of tungsten carbide (FIG. 18). Since the tungsten carbide material is metallurgically distinct from steel material, there is no tendency for metal pickup or galling between the piston and the cylinder. In addition since the deflection of the piston when it is inflated by internal pressure is of a very low order of magniture, there is no tendency to rupture or otherwise separate the tungsten carbide coating from the surface of the piston.

As shown in FIGS. 16 and 17, the fitting of a piston to a cylinder by internal pressure can be applied to piston 239 which is adapted to be used in an internal combustion engine, a compressor, or other devices employing pistons. In FIGS. 16 and 17, piston 239 includes bore 240 through which a wristpin is adapted to be used. End portions 241 and 242 are of substantially heavy sections to insure their dimensional accuracy during operation and during the pressurizing of the piston. Wall portion 243 has a substantially thin section and the material selected for the wall portion can be material that is at least to some extent resilient. Lands 244 comprise a hard material such as a carbide material and more in particular tungsten carbide. As a result lands 244 can provide the sealing and wiping functions which are normally provided by piston rings.

The piston is subjected to internal hydraulic pressure by the introduction of pressure fluid through port 245 and check valve 246. In the case of filling piston 239 with a liquid, the charging pressure can be selected to be compatible with any degree of expansion which the liquid may experience during operation in the cylinder at the normal elevated operating temperature. Since engines, compressors and the like must be provided with some form of cooling for the piston, it can be understood that the liquid or other fluid within the piston operates at a predictable maximum temperature and that consequently compensation for the operating internal pressure can be readily made.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that changes may be made in the details of construction and operation, and in the combination and arrangement of parts, without departing from the spirit and scope of the invention.

What is claimed is:

1. A pump comprising:

(a) a cylinder having an inlet port extending through the wall thereof adjacent one end portion of said cylinder and an exhaust port extending through the wall thereof adjacent the other end portion of said cylinder,

(b) a free piston slidably mounted within said cylinder adjacent said one end portion thereof, said free piston having an inner face directed toward the central portion of said cylinder,

(c) a driven piston slidably mounted within said cylinder adjacent said other end portion thereof, said driven piston having an inner face directed toward said inner face of said free piston,

(d) means for reciprocating said driven piston along a predetermined path of travel, at one end of the predetermined path of travel said inner face of said driven piston being adjacent said exhaust port for exhausting fluid therethrough and in contact with said inner face of said free piston, at the other end of the predetermined path of travel said inner face of said driven piston being adjacent said intake port and spaced apart from the inner face of said free piston to enable fluid to enter said cylinder through said inlet port,

(e) means for urging said free piston toward said driven piston, and

(f) means for limiting the movement of said free piston toward said driven piston to a position in which said inner face of said free piston is between said exhaust port and said inlet port thereby closing said exhaust port,

whereby fluid can be admitted through said intake port and into said cylinder between said inner face of said driven piston and said inner face of said free piston, compressed between said driven piston and said free piston, and discharged through said exhaust port.

2. A pump in accordance with claim 1 in which said cylinder extends vertically in order to reduce the loading of said free piston and said driven piston with respect to the inner surface of said cylinder.

3. A pump in accordance with claim 1 in which at least one of said free piston and said driven piston comprises:

(a) structure forming a hollow enclosed cylinder having a nominal outside diameter substantially corresponding to the inside diameter of said cylinder, and

(b) means for applying a controlled force to at least a portion of the interior of said hollow cylinder to expand the outside diameter thereof to a predetermined dimension,

whereby the fit between at least one of said free piston and said driven piston can be determined.

4. A pump in accordance with claim 3 in which said structure forming a hollow enclosed cylinder comprises:

(a) a tubular side wall portion, the thickness of said side wall portion being sufliciently thin to enable said side wall portion to be expanded by the application of controlled force to at least a portion thereof; and

(b) a pair of end walls each connected to a different opposite end of said tubular side wall portion, the thickness of said pair of end walls being sufl'iciently thick to prevent said end walls from appreciably defleeting and to confine the deflection of said structure forming a hollow enclosed cylinder substantially to the expansion of said tubular side wall.

5. A pump in accordane with claim 3 in which said means for applying a controlled force to at least a portion of the interior of said hollow cylinder comprises a valve connected to said interior of said hollow cylinder for introducing a pressured fluid thereinto.

6. A pump in accordance with claim 3 in which said means for applying a controlled force to at least a portion of the interior of said hollow cylinder comprises a pressured fluid disposed Within said interior of said hollow cylinder.

7. A pump in accordance with claim 6 in which said pressure fluid disposed within the interior of said hollow cylinder comprises a pressured hydraulic liquid.

8. A pump in accordance with claim 1 in which at least one of said free piston and said driven piston is provided with a coating on the surface thereof contacting said cylinder, said coating being adapted to decrease wear between said one piston and said cylinder.

9. A pump in accordance with claim 8 in which said coating is at least one from the group comprising the refractory hard metals.

10. A pump in accordance with claim 8 in which said coating is alumina material.

11. A pump in accordance with claim 1 in which at least one of said free piston and said driven piston are formed from alumina material- 12. A pump in accordance with claim 1 in which said means for reciprocating said driven piston along a predetermined path of travel comprises a double-acting pressured fluid actuator connected to said driven piston.

13. A pump in accordance with claim 1 in which said means for reciprocating said driven piston along a predetermined path of travel comprises a scotch-yoke mech anism connected to each of said driven pistons.

14. A pump in accordance with claim 1 in which said means for urging said free piston toward said driven piston comprises a bounce chamber in communication with the outer face of said free piston.

15. A pump in accordance with claim 14 in which said bounce chamber contains an elastic fluid.

16. A pump in accordance with claim 1 in which said means for limiting the movement of said free piston toward said driven piston comprises a rod connected to the outer faced free piston and means engaging said cylinder for terminating the movement of said rod toward said driven piston when said free piston is between said exhaust port and said inlet port.

17. A pump in accordance with claim 16 in which said means engaging said cylinder for terminating the movement of said rod toward said driven piston is resilient.

18. A pump comprising:

(a) pair of assemblies including:

(1) a cylinder having an inlet port extending through the wall thereof adjacent one end portion of said cylinder and an exhaust port extending through the wall thereof adjacent the other end portion of said cylinder,

(2) a free piston slidably mounted within said cylinder adjacent said other end portion thereof, said free piston having an inner face directed toward the central portion of said cylinder,

(3) a driven piston slidably mounted within said cylinder adjacent said other end portion thereof, said driven piston having an inner face directed toward said inner face of said free piston,

(4) means for urging said free piston toward said driven piston, and

(5) means for limiting the movement of said free piston toward said driven piston to a position in which said inner face of said free piston is between said exhaust port and said inlet port thereby closing said exhaust port, each of said assemblies enabling fluid to be admitted through said intake port and into said cylinder between said inner face of said driven piston and said inner face 13 of said free piston, compressed between said driven piston and said free piston, and discharged through said exhaust port;

(b) means for supporting said cylinder of each of said pair of assemblies along a common line extending along the longitudinal axis of each of said cylinders, said cylinders of said pair of assemblies extending opposite to one another; and

(c) means for reciprocating each of said driven pistons along a predetermined path of travel, said pistons being reciprocated in synchronism with one another with said driven piston of one of said pair of assem'blies being approximately 180 out of phase with the other of said pair of assemblies, at one end of the predetermined path of travel of each of said driven pistons said inner face of said driven piston being adjacent said exhaust port for exhausting fluid therethrough and in contact with said inner face of said free piston, at the other end of the predetermined path of travel said inner face of said driven piston being adjacent said intake port and spaced apart from the inner face of said free piston to enable fluid to enter said cylinder through said inlet port.

19. A pump in accordance with claim 18 in which said means for reciprocating each of said driven pistons along a predetermined path of travel comprises a pressurized fluid actuator connected to each of said driven pistons.

20. A pump in accordance with claim 18 which said means for reciprocating each of said driven pistons along a predetermined path of travel comprises a scotch-yoke mechanism connected to each of said driven pistons.

21. A pump in accordance with claim 18 in which said means for reciprocating each of said driven pistons along a predetermined path of travel comprises:

(a) a double-acting fluid pressure actuator having each of the opposite portions of said actuator connected to said driven pistons of different ones of said cylinders of said pair of assemblies, and

(b) means for alternately delivering pressured fluid to the different opposite end portions of said doubleacting fluid pressure actuator for reciprocating said actuator and thereby said driven pistons connected thereto.

22. A pump in accordance with claim 21 in which said means for alternately delivering pressured fluid to the diflerent opposite end portions of said double-acting fluid pressure actuator comprises:

(a) a valve means adapted to be connected to a source of pressured fluid for alternately directing pressured fluid to the diflerent opposite end portions of said double-acting fluid pressure actuator, and

('b) mean for operating said valve to alternately direct pressured fluid to the diflerent opposite sides of said actuator.

23. A pump in accordance with claim 22 in which said means for operating said valve to alternately direct pressured fluid to the diflierent opposite sides of said actuator comprises means coupled to said valve for positioning said valve in response to the operation of said means of each of said pair of assemblies for urging said free piston toward said driven piston.

24. A pump in accordance with claim 23:

(a) in which said means of each of said pair of assemblies for urging said free piston toward said driven piston comprises a bounce chamber, and

(b) in which said means for positioning said valve in response to the operation of said means for urging said free piston toward said driven piston is responsive to the operation of said bounce chamber of each of said pair of assemblies.

25. A pump in accordance with claim 24:

(a) in which said bounce chamber contains an elastic fluid, and

(b) in which said means for positioning said valve in response to the operation of the bounce chamber is responsive to the pressure changes within the bounce chamber of each of said pair of assemblies.

26. A pumpin accordance with claim 21 in which said means for alternately delivering pressured fluid to the difierent opposite end portions of said double-acting fluid pressure actuator comprises an additional pump adapted to be alternately connected to the different opposite end portions of said doubleacting fluid pressure actuator to deliver pressure fluid thereto.

27. A pump in accordance with claim 26 in which said additional pump comprises:

(a) an additional double-acting fluid pressure actuator, the opposite end portions of said additional actuator being respectively connected to the opposite end portions of said double-acting fluid pressure actuator connected to said driven pistons, and

(b) means for reciprocating said additional actuator to pump pressured fluid alternately to said actuator; whereby said actuator and said driven pistons connected thereto are reciprocated.

28. A pump in accordance with claim 27 in which said means for reciprocating said additional actuator to pump pressured fluid to said actuator comprises means responsive to the movement of at least one of said free pistons for alternately applying pressured fluid to the opposite end portions of said additional actuator to control the reciprocation of said additional actuator.

29. A pump in accordance with claim 18 in which said means for limiting the movement of said free piston toward said driven piston comprises a rod connected to said free piston and means for terminating the movement of said rod in the direction of said driven piston when said inner face of said free piston is between said exhaust port and said inlet port.

30. A pump in accordance with claim 27 in which said means for reciprocating said additional actuator to pump pressured fluid to said actuator comprises means responsive to the movement of at least one of said free pistons for controlling said reciprocating means.

31. pump in accordance with claim 18 and further comprising:

(a) additional means for selectively connecting the opposite end portions of said additional doubleacting fluid pressure actuator to the respective opposite end pogtions of said double-acting fluid pressure actuator, an

(b) means responsive to the movement of a least one of said free pistons for actuating said additional means to selectively connect the opposite end portions of said additional double-acting fluid pressure actuator to the respective opposite end portions of said double acting fluid pressure actuator,

whereby said driven pistons are driven in response to the movement of at least one of said free pistons.

32. A pump in accordance with claim 18 in which said means for supporting said cylinder of each of said pair of assemblies along 'a common line support said cylinders along a substantially vertical common line, whereby the forces applied to the wall of said cylinders of each of said pair of assemblies is reduced.

33. A pump in accordance with claim 18 and further comprising means for connecting said exhaust port of said cylinder of one of said pair of assemblies to said inlet port of said cylinder of the other of said pair of assemblies, whereby one cylinder of said pair of assemblies can be serially connected to the other cylinder of said pair of assemblies.

34. A pump in accordance with claim 18 (a) in which said means for urging said free piston to- 1 5 1s ward said driven piston of each of said pair of assem- References Cited blies comprises a bounce chamber, and UNITED STATES PATENTS b h' h d d t d in w 1c means are PIOVl e for connec mg sai 1,564,215 12/1925 Dimg 1O3 171 R bounce chamber chambers of each of said pair of 3 068 794 2 1 assemblies to one another for fluid flow therebetween, 5 96 Morns et a 103 44 XR whereby said connecting means enables the fluid ROBERT W ALKER, Primary Examiner flow therein to assist in maintaining said free pistons in proper synchronism with said driven US. Cl. X.R. piston. 10 230180 ($33? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 H Q29 Dated October 7. 1069 Inventoz-(s) ELMAN B. MYERS Column 3, line 55 "whish" should be which Column 4, line 37 "will should be wall Column 5, line 44 "tthe" should be the Column 7, line 70 "inlet" should be Inlet Column 8, line 33 "bolt" should be bolts Column 8, line 49 "tolerance" should be tolerances Column 12, line 1 'accordane should be accordance Column 13, line 28 "pressurized" should be pressured Column 13, line 56 "mean" should be means Column la, line 13 "doubleacting" should be doublea.cting Column 14, line +8 "doubleacting" should be double-acting SIGNED AND SEALED JUN2 197g Amt:

Edward M. Fletcher. It. wmnu 3 Meeting Offioer 1013510116:- or ga 

